The present disclosure relates generally to medical devices and, more particularly, to sensors used for sensing physiological parameters of a patient.
This section is intended to introduce the reader to aspects of the art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
In the field of medicine, doctors often desire to monitor certain physiological characteristics of their patients. Accordingly, a wide variety of devices and techniques have been developed for monitoring physiological characteristics. Such devices and techniques provide doctors and other healthcare personnel with the information they need to provide the best possible healthcare for their patients. As a result, these monitoring devices and techniques have become an indispensable part of modern medicine.
One such monitoring technique is commonly referred to as pulse oximetry. Pulse oximetry may be used to measure various blood flow characteristics, such as the blood-oxygen saturation of hemoglobin in arterial blood and/or the rate of blood pulsations corresponding to each heartbeat of a patient.
The devices based upon pulse oximetry techniques are commonly referred to as pulse oximeters. Pulse oximeters typically utilize a non-invasive sensor that is placed on or against a patient's tissue that is well perfused with blood, such as a patient's finger, toe, forehead or earlobe. The pulse oximeter sensor emits light and photoelectrically senses the absorption and/or scattering of the light after passage through the perfused tissue. A photo-plethysmographic waveform, which corresponds to the cyclic attenuation of optical energy through the patient's tissue, may be generated from the detected light. Additionally, one or more physiological characteristics may be calculated based upon the amount of light absorbed or scattered. More specifically, the light passed through the tissue may be selected to be of one or more wavelengths that may be absorbed or scattered by the blood in an amount correlative to the amount of the blood constituent present in the blood. The amount of light absorbed and/or scattered may then be used to estimate the amount of blood constituent in the tissue using various algorithms.
For example, a reflectance-type sensor placed on a patient's forehead may emit light into the skin and detect the light that is “reflected” back after being transmitted through the forehead tissue. A transmission-type sensor may be placed on a finger; wherein the light waves are emitted through and detected on the opposite side of a finger. In either case, the amount of light detected may provide information that corresponds to valuable physiological patient data. The data collected by the sensor may be used to calculate one or more of the above physiological characteristics based upon the absorption or scattering of the light. For instance, the emitted light is typically selected to be of one or more wavelengths that are absorbed or scattered in an amount related to the presence of oxygenated versus de-oxygenated hemoglobin in the blood. The amount of light absorbed and/or scattered may be used to estimate the amount of the oxygen in the tissue using various algorithms.
The sensors generally include an emitter that emits the light and a detector that detects the light. The emitter and detector may be located on a flexible circuit that allows the sensor to conform to the appropriate site on the patient's skin, thereby making the procedure more comfortable for a patient. During use, the emitter and detector may be held against the patient's skin to facilitate the light being directed into and received from the skin of the patient. For example, the sensor may be applied to a patient's forehead. To aid in the sensor's proper placement and the proper application of pressure by the sensor to the forehead site, some forehead sensors are maintained at the forehead site by either the assistance of an adhesive layer, a headband or a hat. Any number of methods may be used to press the sensor against the patient's skin to facilitate the light being directed into and received from the skin of the patient.
A properly fitted sensor will allow the emitted light to travel through the tissue of the site and be detected without additional light being introduced, thereby preventing measurement distortion. However, in practice, the design of the sensor may not provide a tight fit between the sensor and the surface of the patient's skin. Further, to reduce measurement error, protective layers may be applied to the sensors to prevent external light from being detected by the sensor. In certain places on the flexible circuit, protective layers may delaminate, leading to shunting, where light is transmitted directly between the emitter and detector, leading to inaccurate measurements. In addition, layers added to the sensor may be uncomfortable to the patient, especially if they are delaminating.
Moreover, to increase accuracy, a photodetector of the sensor may be encompassed by a layer of wire mesh to shield the photodetector from external electromagnetic fields. The wire mesh layer may contribute to the delamination of the light blocking layer, exacerbating the shunting and measurement issues. Further, proper application of the light-blocking layer and the wire mesh layer can be time consuming. There is a need, therefore, for an improved arrangement for blocking external light and external static fields that will improve accuracy and comfort of the sensor.